JSON parser does not handle 64-bit numbers correctly

[naquin]

When you give a number that is greater than 2^32, the JSON parser converts it to a 32-bit integer. The following code illustrates:

std::string json = "{ \"test\" : 5000000000000000 }";
Parser parser;
Var result;

try
{
    DefaultHandler handler;
    parser.setHandler(&handler);
    parser.parse(json);
    result = handler.result();
}
catch(JSONException& jsone)
{
    std::cout << jsone.message() << std::endl;
    assert(false);
}

assert(result.type() == typeid(Object::Ptr));

Object::Ptr object = result.extract<Object::Ptr>();
Var test = object->get("test");
assert(test.isInteger());
Int64 value = test;
assert(value == 5000000000000000); // fails here, value gets truncated